Microelectronic devices containing vacuum chambers or cavities are presently used for a number of applications including incandescent light sources, sensors, vacuum FET and vacuum tube on a chip device. The publication VACUUM-SEALED SILICON MICROMACHINED INCANDESCENT LIGHT SOURCE by C. H. Mastrangelo and R. S. Muller, IDEM 1989, pgs. 503-506 describes a vacuum-sealed silicon-filament incandescent light wherein a doped polysilicon filament wire with silicon nitride is enclosed in a vacuum sealed cavity with a silicon substrate. The cavity is an anisotropically-etched v-groove in the silicon substrate. A silicon nitride window over the V-groove hermetically seals the cavity after the filament is placed within.
The publications MICRO-DIAPHRAGM PRESSURE SENSOR by S. Sugiuam et al., IDEM 1986, pgs. 184-185 and FABRICATION TECHNIQUES FOR INTEGRATED SENSOR MICROSTRUCTURES by H. Guckel and D. W. Burns, IDEM 1986 pgs. 176-179 describe the use of vacuum cavities in micromechanical sensors wherein a cavity is etched in a silicon wafer, covered and sealed with a diaphragm and a vacuum is created in the cavity. In the publication THE COMEBACK OF THE VACUUM TUBE: SEMICONDUCTOR VERSIONS SUPPLEMENT TRANSISTORS? by Kathy Skidmore, Semiconductor International, August 1988, pgs. 15-17 a dielectric layer is etched to provide a cavity in which a metal emitter is located, a metal gate is formed above the emitter and a metal anode layer is fabricated over and seals the cavity, in which a vacuum is then created.
In all of the above devices and structures, the vacuum is created after the cavity is sealed by the application of an external vacuum pump. The external vacuum is typically produced in the fabrication process which seals the cavity (i.e. PECVD SiO.sub.2) hence the vacuum in the cavity is contaminated by the gases used in the process and is only as low in pressure as that used in the process.